Typically, in Li—S batteries, Li metal anodes are used. These lead to high capacities and are easily producible, however a few disadvantages are associated therewith. Li metal is very reactive and, in the production and in the use of the cells, can lead to safety problems (so-called “thermal run-away” from the melting point of 181° C. for metallic lithium). Furthermore, Li metal is susceptible to dendritic growth during cycling, as a consequence of which the result is a great increase in the surface area and an increase in reactivity.
In addition, as a result of the grown dendrites, short circuits in the cell can be produced, which leads to destruction of the cell and also to additional safety problems. Finally, the cycle stability is generally limited, when using metallic lithium, above all because of the dendritic growth of lithium, to 100 to at most 200 cycles.
In order to solve this problem, graphite anodes have been used in Li batteries to date. The stability and safety could hence be crucially improved, however at the cost of lower capacity of the batteries. For a sulphur battery, the problem occurs that graphite anodes are not possible for various reasons. As an example of this, the intercalation of solvent of the sulphur electrolyte can be mentioned, which leads to the destruction of the graphite anode.
Initial approaches show the potential for replacing the lithium anode with alloy anodes (Si, Sn) with a very high capacity. These alloy anodes in fact in principle solve the problems which are associated with Li dendrites, but to date have also not been particularly cycle-stable. The high expansion of Si (and Sn) which is caused by the lithiation is hereby problematic. The expansion is for example 320% for Si and 260% for Sn (Zhang, W.-J., Journal of Power Sources, 196: 13-24, 2011).
Production of good Si and Sn anodes (above all for Li ion cells) is the subject of current research. Publications relating to Si and Sn in Li—S cells show the applicability in principle of these alloy anodes but verify the cycle instability of these systems. The reason for the cycle instability is generally degradation effects on the anode- and also cathode side.
Difficulties occur also from the lithiation either of the anode or of the cathode. Thus, only a very low partial lithiation and hence low capacity was able to be achieved if copper was used as carrier substrate and current conductor for an anode material (e.g. silicon thin film) (Elazari, R. et al., Electrochemistry Communications, 14: 21-24, 2012). For an anode made of silicon nanowire, likewise only a very low capacity could be achieved (Yang, Y. et al., Nano Letters, 10: 1486-1491, 2010).
Furthermore, when using a cathode made of carbon-sulphur composite material and a lithiated anode made of carbon-silicon composite material, a high capacity of approx. 300 mAh/g could be achieved but only low stability could be attained.
Also Li—S cells based on Li metal anodes in which particularly complex coating of lithium was used are known (U.S. Pat. No. 7,358,012 B2).